Treasury Secretary Steve Mnuchin recently told Congress he would be happy to provide information about Internal Revenue Service audits of presidents ― a task the agency performs every year. But when he was asked for those details on Wednesday, he didn’t have the answers.

Sen. Chris Van Hollen (D-Md.) asked Mnuchin during a hearing if the mandatory presidential audit would encompass previous tax years if the person who became president had been under audit for those years.

“I don’t know the answer to that but I can look into it,” Mnuchin said. “I do know the audit requirements are of the current years, but I’d be happy to look to look into that issue and get back to you.”

Mnuchin’s inability to answer such a basic question about the IRS’ presidential audits comes on the heels of his refusal to comply with a federal law allowing congressional tax-writing committees to obtain any person’s tax returns.

House Ways & Means Committee Chairman Richard Neal (D-Mass.) requested Mnuchin and the IRS provide copies of the past six years of Trump’s tax returns in April. Neal’s request stated the committee’s interest in conducting oversight of the IRS’s routine audits of presidential tax returns. The IRS has audited every president’s taxes since a congressional investigation found that President Richard Nixon severely underpaid his taxes.

Mnuchin rejected Neal’s lawful request by insinuating that the committee’s interest in IRS presidential tax audits was merely a pretext to obtain and disseminate Trump’s tax returns for partisan political purposes. If Democrats really wanted to know about presidential audits, Mnuchin said in a letter last month, “we would be happy to accommodate that interest by providing additional information on the audit process.”

Van Hollen said Wednesday, “The fact that it’s difficult for you to answer that question underscores the congressional concern about whether or not the tax laws are being fairly applied.”

Since 1977 the IRS has had a policy of auditing the president every year so that the decision to do so never falls on individual officials, who could feel pressure to make the decision one way or the other. The IRS put the policy in place after a congressional investigation a few years earlier revealed that even though the IRS had said Nixon had paid his federal income taxes, he actually owed hundreds of thousands of dollars.

Nixon while in office had voluntarily given his tax returns to Congress after questions arose about deductions he had taken, and every president since then has voluntarily made his tax returns public ― except Trump.

The president bragged last week that he used business losses as “tax shelter” to avoid paying any federal taxes for several years during his real estate career. He added that real estate developers considered it “sport” to avoid paying taxes.

Van Hollen asked another question of Mnuchin: Does the presidential audit include both the president’s personal and business tax returns?

Mnuchin again didn’t answer. “As it relates to the specifics of the audit requirements, again I would be happy, in a smaller, non-public setting, to go through with the appropriate congressional members what exactly the audit procedures are,” he said.

Van Hollen said he thought the answer should be public.

Having been rebuffed by Mnuchin, Neal issued a subpoena on Friday to the Treasury secretary and IRS commissioner for the tax documents his committee seeks. Mnuchin said he would probably disobey the subpoena, at which point Democrats can ask a federal court to enforce it. The court process could take months or years.

“If this issue goes through the courts I think it’s better that we have the court’s interpretation… than establish a precedent that is weaponizing the IRS,” Mnuchin said.